A8514KLPTR-T Allegro Microsystems Inc, A8514KLPTR-T Datasheet - Page 28

• Manufacturer Part Number: A8514KLPTR-T
• Description: IC LED DVR WHT 4X80MA 16-ETSSOP
• Manufacturer: Allegro Microsystems Inc

Specifications of A8514KLPTR-T

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

A8514
The reverse voltage rating should be such that during operation
condition, the voltage rating of the device is larger than the maxi-
mum output voltage. In this case it is V
The peak current through the diode is calculated as:
The third major component in deciding the switching diode is
the reverse current characteristic of the diode. This characteristic
is especially important when PWM dimming is implemented.
During PWM off-time the boost converter is not switching. This
results in a slow bleeding off of the output voltage, due to leakage
currents. I
cially at high temperatures. On the diode that was selected in this
design, the current varies between 1 and 100 μA.
Step 7
must be chosen such that they can provide filtering for both the
boost converter and for the PWM dimming function. The biggest
factors that contribute to the size of the output capacitor are:
PWM dimming frequency and PWM duty cycle. Another major
contributor is leakage current, I
tion of the OVP current sense as well as the reverse current of the
switching diode. In this design the PWM dimming frequency is
200 Hz and the minimum duty cycle is 1%. Typically, the voltage
variation on the output, V
be less than 250 mV, so that no audible hum can be heard. The
capacitance can be calculated as follows:
A capacitor larger than 8.71 μF should be selected due to deg-
radation of capacitance at high voltages on the capacitor. Two
ceramic 4.7 μF 50 V capacitors are a good choice to fulfill this
requirement. Corresponding capacitors include:
C
OUT
Choosing the output capacitors. The output capacitors
Vendor
Murata
Murata
R
=
=
, or reverse current, can be a large contributor, espe-
I
dp
I
440 μA
LK
= I
= 0.94 (A) + 0.37 (A) / 2 = 1.13 A
IN
4.7 μF 50 V
2.2 μF 50 V
(max) +
f
Value
PWM(dimming)
COUT
200 Hz
1 – D(min)
1
/
, during PWM dimming must
1 – 0.01
2
LK
ΔI
. This current is the combina-
GRM32ER71H475KA88L
GRM31CR71H225KA88L
LUSED
0.250 V
V
COUT
OUT(OVP)
Part number
=
8.71 μF
.
Wide Input Voltage Range, High Efficiency
(22)
(23)
The rms current through the capacitor is given by:
The output capacitor must have a current rating of at least
420 mA. The capacitor selected in this design was a 4.7 μF 50 V
capacitor with a 3 A current rating (two used).
Step 8
selected such that it provides a good filtering of the input voltage
waveform. A good rule of thumb is to set the input voltage ripple
ΔV
input capacitor requirements are as follows:
The rms current through the capacitor is given by:
A good ceramic input capacitor with ratings of 2.2 μF 50 V or
4.7 μF 50 V will suffice for this application. Corresponding
capacitors include:
I
COUT
IN
C
to be 1% of the minimum input voltage. The minimum
IN
Selecting input capacitor. The input capacitor must be
rms =
C
Vendor
Murata
Murata
rms =
IN
=
=
=
=
Fault Tolerant LED Driver
0.240
I
8
8
OUT
0.240 (A) ×
I
OUT
(1 – D)×
(1 – 0.75)×
2 (MHz) 0.1 (V)
4.7 μF 50 V
2.2 μF 50 V
f
SW
∆I
Value
×
0.37 (A)
D(max) +
Lused
0.75 +
I
IN
∆I
∆V
(max)
115 Northeast Cutoff
1.508.853.5000; www.allegromicro.com
Allegro MicroSystems, Inc.
Worcester, Massachusetts 01615-0036 U.S.A.
Lused
12
0.927 (A)
1 – D(max)
0.37 (A)
IN
1 – 0.75
0.94 / 12
12
I
GRM32ER71H475KA88L
GRM31CR71H225KA88L
IN
0.37
(max)
∆I
Lused
=
Part number
=
0.11 A
/ 12
0.23 μF
=
0.42 A
(24)
(25)
(26)
28